"to prevent some Pugachov"
was a deserter from the Russian Army who led a peasant rebellion in eighteenth century Russia, during Catherine the Great's reign. Although he was actually the son of a Don Cossack landowner he claimed that he was Tsar Peter III, who had been assassinated. His rebellion attracted many serfs, as he announced that he would abolished serfdom upon seizing the throne. His rebellion was crushed at Tsaritsyn in 1774, and he was caught and executed the following year.
Alexander Pushkin was fascinated with Pugachev's story. He wrote a history of the rebellion, and a novella, The Captain's Daughter, which is set at the time.